Retroreflective materials have the ability to redirect light incident on the material back toward the originating light source. This property has led to the widespread use of retroreflective sheeting for a variety of traffic and personal safety uses. Retroreflective sheeting is commonly employed in a variety of articles (e.g., road signs, barricades, license plates, pavement markers, and pavement marking tape, as well as retroreflective tapes for vehicles and clothing).
There are generally two types of retroreflective sheeting: beaded sheeting and cube-corner sheeting. Beaded sheeting typically employs a multitude of glass or ceramic microspheres to retroreflect incident light. Cube-corner sheeting, on the other hand, typically employs a multitude of rigid, interconnected, cube-corner elements to retroreflect incident light. Cube-corner retroreflective sheeting, sometimes referred to as “prismatic” sheeting, typically comprises a thin transparent layer having a substantially planar first surface and a second structured surface comprising a plurality of geometric structures. In truncated cube-corner sheeting some or all geometric structures include three reflective faces configured as a cube-corner element.
The base edges of adjacent cube-corner elements of truncated cube-corner arrays are typically coplanar. Other cube-corner element structures, described as “full cubes” or “preferred geometry” typically comprise at least two non-dihedral edges that are not coplanar. Such structures typically exhibit a higher total light return in comparison to truncated cube-corner elements. Cube-corner sheeting having “preferred geometry” cube-corner elements may be manufactured by a laminae process (see, e.g., U.S. Pat. No. 7,156,527 (Smith)).
Cube-corner retroreflective sheeting is commonly produced by first manufacturing a molding tool that has a structured surface, wherein the structured surface corresponds either to the desired cube-corner element geometry in the finished sheeting or to a negative (inverted) copy thereof, depending upon whether the finished sheeting is to have cube-corner pyramids or cube-corner cavities (or both). The molding tool is then replicated using any suitable technique such as conventional nickel electroforming to produce tooling for forming cube-corner retroreflective sheeting by processes such as embossing, extruding, or cast-and-curing.
Alternative retroreflective articles and alternative methods for making retroreflective articles are desirable.